Vigorous physical training, either independently or in conjunction with factors such as weight, body composition and/or energy intake, is associated with various disruptions in ovarian function, including oligo/amenorrhea, shortened luteal phase, lengthened follicular phase, anovulation, and decreased progesterone and estrogen. These alterations may have beneficial consequences in terms of breast and other reproductive cancers, but negative consequences in terms of bone health. The extent to which ovarian disruption is associated with the recreational and occupational activity typically seen in the population at large is not well known. This proposal is for a series of epidemiological studies that will examine the influence of physical activity on characteristics of the menstrual cycle, reproductive hormonal patterns, and hormone-related symptoms using three different datasets. The first dataset is from the prospective component of the Semiconductor Health Study, a large study of the risk of adverse reproductive outcomes among women working in silicon wafer manufacturing plants. The sample consists of 402 ethnically diverse women who were interviewed at baseline and who completed daily diaries and collected daily urine specimens for up to six months. The second dataset is from a community-based longitudinal cohort study of bone health in women from Tecumseh, Michigan (N=583). For four years, data on physical activity, weight, body composition, dietary intake, and symptoms were collected annually and menstrual calendars monthly. The longitudinal nature of this dataset allows for an examination of the relationship between change in activity and change in menstrual function and symptoms over time, taking into account the influence of weight, body composition and dietary factors. Finally, a case-control study of diet and premenstrual syndrome with 102 cases and 102 matched controls conducted at the Northern California Kasier Permanente Medical Care Program provides data for an evaluation of the risk of diagnosed PMS associated with activity. Data will be evaluated using cross-sectional and longitudinal analytic techniques. By furthering understanding of the relation between physical activity and ovarian function at the population level, this proposed study will contribute to a better understanding of the benefits and risks of physical activity for women's reproductive and overall health.